Automobile engines produce torsionals or vibrations that are undesirable to transmit through the vehicle transmission. To isolate such torsionals, torsional dampers can be implemented into the vehicle transmission. These dampers rest between the engine crankshaft and the input shaft or turbine shaft of the transmission to substantially counteract the unwanted torsionals generated by the engine. Dampers are configured with springs that have the capacity to carry maximum engine torque plus some margin above.
One premise behind hybrid automobiles is that alternative power is available to propel the vehicle, thus reliance on the engine for power can be decreased, thereby increasing fuel economy. Since hybrid vehicles can derive their power from sources other than the engine, hybrid engines typically operate at lower speeds more often and can be turned off while the vehicle is propelled by the electric motors. For example, electrically-variable transmissions alternatively rely on electric motors housed in the transmission to power the vehicle's driveline. Engines in hybrid vehicles are therefore required to start and stop more often than engines in non-hybrid systems. Compression pulses are generated by the engine during starts and stops that can produce undesirable vibration in hybrid vehicles such as those having an electrically-variable transmission. Therefore, greater functionality is desirable in the damper assembly to aid the electrically-variable transmission in canceling these compression pulses.
Lastly, when the internal combustion engine is not operating, pumps which derive their power from the engine are also inoperable. Where hydraulic fluid is used to govern the torsional damper, the fluid is subjected to centrifugal loading as a result of the high annular speeds at which the torsional damper rotates.